People with a mental disease cannot join the Australian Army, Navy or Air Force in any uniformed capacity. They can, however, join the Australian Public Service (APS) and work for the Department of Defence in an Administrative role.
As of 2011, gay people can freely join the US military and do not have to hide their orientation.
Yes
No, you cannot.
Not in the US military, no.
Sir Yes, Sir!!
U.S army
Yes. You can join the US military without being a citizen, so long as you've established permanent residence and have declared an intent to obtain citizenship.
One can join the US military as young as seventeen (17) with parental consent
The Coast Guard is a branch of the US Military, so yes.
No - the minimum age to join any branch of the military is 17, and only with parental permission (signature on your entrance application). Those who are younger can of course join the various military schools and cadet programs around the country in preparation for later military careers.
In the Canadian Forces, yes. In the US Army, you need parental consent to join at 17, but you can't join at 16.
Joining the military in the US is voluntary. He doesn't have to join if he doesn't want to.